Multiply Confined Nickel Nanocatalysts Produced by Atomic Layer Deposition for Hydrogenation Reactions

To design highly efficient catalysts, new concepts for optimizing the metal–support interactions are desirable. Here we introduce a facile and general template approach assisted by atomic layer deposition (ALD), to fabricate a multiply confined Ni‐based nanocatalyst. The Ni nanoparticles are not only confined in Al₂O₃ nanotubes, but also embedded in the cavities of Al₂O₃ interior wall. The cavities create more Ni–Al₂O₃ interfacial sites, which facilitate hydrogenation reactions. The nanotubes inhibit the leaching and detachment of Ni nanoparticles. Compared with the Ni‐based catalyst supported on the outer surface of Al₂O₃ nanotubes, the multiply confined catalyst shows a striking improvement of catalytic activity and stability in hydrogenation reactions. Our ALD‐assisted template method is general and can be extended for other multiply confined nanoreactors, which may have potential applications in many heterogeneous reactions.     

组合型Pt3Sn/Al2O3催化剂用于芳香硝基化合物一锅法合成N-烷基芳胺

采用吸附法制备了组合型Pt₃Sn/Al₂O₃双金属催化剂, 将该催化剂用于芳香硝基化合物原位液相加氢一锅法合成N-烷基芳胺. 研究表明, 在503 K, 空速为7.5 h^-1, 水体积分数为5%时, 1%(质量分数)Pt₃Sn/Al₂O₃催化剂具有较高的催化性能, 硝基苯的转化率为100%, N-乙基苯胺和N,N-二乙基苯胺的总选择性为98.2%. 同时,该催化剂对原位液相加氢烷基化反应具有一定普适性, 本文研究的14 种芳香硝基化合物与低级脂肪醇反应,均具有较高的N-烷基化产率.     

Highly selective catalysts for liquid-phase hydrogenation of substituted alkynes based on Pd—Cu bimetallic nanoparticles

Catalytic properties of Pd—Cu bimetallic catalysts supported on SiO₂ and Al₂O₃ were studied in a model reaction of selective hydrogenation of diphenylacetylene. Application of PdCu₂(AcO)₆ heterobimetallic acetate complex as a precursor made it possible to obtain homogeneous Pd—Cu bimetallic nanoparticles. This result was supported by the data of IR spectroscopy of adsorbed CO. The Pd-Cu catalysts showed considerably higher selectivity than monometallic samples. Moreover, the introduction of copper decreases the hydrogenation rate of diphenylethylene (DPE) to diphenylethane. As a result, the maximum yield of the target product, DPE, increased from 78 to 93% in the presence of Pd—Cu catalysts.     

Role of metal Cu species on methyl laurate catalytic hydrogenation to oxygen-containing compounds

The Cu/γ-Al₂O₃ catalysts with different Cu loadings were prepared by impregnation method. The physicochemical properties of these Cu/γ-Al₂O₃ catalysts were characterized by H₂-TPR, XRD, and in-situ XPS. The catalytic hydrogenation performances of methyl laurate over Cu/γ-Al₂O₃ catalysts were studied. The results show that the hydrogenation performances of methyl laurate on Cu/γ-Al₂O₃ catalyst are related to the dispersion, crystallite size, and content of the active component Cu⁰. The 10CA catalyst has the best hydrogenation performances for methyl laurate to produce C₁₂ alcohol. At 300 °C, the conversion of methyl laurate and the selectivity of C₁₂ alcohol are 55.6% and 30.4%, respectively.     

Development of high performance Cu/ZnO-based catalysts for methanol synthesis and the water-gas shift reaction

Our groups studies on Cu/ZnO-based catalysts for methanol synthesis via hydrogenation of CO₂ and for the water-gas shift reaction are reviewed. Effects of ZnO contained in supported Cu-based catalysts on their activities for several reactions were investigated. The addition of ZnO to Cu-based catalyst supported on Al₂O₃, ZrO₂ or SiO₂ improved its specific activity for methanol synthesis and the reverse water-gas shift reaction, but did not improve its specific activity for methanol steam reforming and the water-gas shift reaction. Methanol synthesis from CO₂ and H₂ over Cu/ZnO-based catalysts was extensively studied under a joint research project between National Institute for Resources and Environment (NIRE; one of the former research institutes reorganized to AIST) and Research Institute of Innovative Technology for the Earth (RITE). It was suggested that methanol should be produced via the hydrogenation of CO₂, but not via the hydrogenation of CO, and that H₂O produced along with methanol should greatly suppress methanol synthesis. The Cu/ZnO-based multicomponent catalysts such as Cu/ZnO/ZrO₂/Al₂O₃ and Cu/ZnO/ZrO₂/Al₂O₃/Ga₂O₃ were highly active for methanol synthesis from CO₂ and H₂. The addition of a small amount of colloidal silica to the multicomponent catalysts greatly improved their long-term stability during methanol synthesis from CO₂ and H₂. The purity of the crude methanol produced in a bench plant was 99.9 wt% and higher than that of the crude methanol from a commercial methanol synthesis from syngas. The water-gas shift reaction over Cu/ZnO-based catalysts was also studied. The activity of Cu/ZnO/ZrO₂/Al₂O₃ catalyst for the water-gas shift reaction at 523 K was less affected by the pre-treatments such as calcination and treatment in H₂ at high temperatures than that of the Cu/ZnO/Al₂O₃ catalyst. Accordingly, the Cu/ZnO/ZrO₂/Al₂O₃ catalyst was considered to be more suitable for practical use for the water-gas shift reaction. The Cu/ZnO/ZrO₂/Al₂O₃ catalyst was also highly active for the water-gas shift reaction at 673 K. Furthermore, a two-stage reaction system composed of the first reaction zone for the water-gas shift reaction at 673 K and the second reaction zone for the reaction at 523 K was found to be more efficient than a one-stage reaction system. The addition of a small amount of colloidal silica to a Cu/ZnO-based catalyst greatly improved its long-term stability in the water-gas shift reaction in a similar manner as in methanol synthesis from CO₂ and H₂.     

Highly Selective Pd–Cu/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for Liquid-Phase Hydrogenation: The Influence of the Pd: Cu Ratio on the Structure and Catalytic Characteristics

The structure and catalytic characteristics of a series of Pd–Cu/α-Al₂O₃ catalysts with Pd: Cu ratio varied from Pd₁–Cu_0.5 to Pd₁–Cu₄ were studied. The use of α-Al₂O₃ with a small surface area (S_sp = 8 m²/g) as a support made it possible to minimize the effect of diffusion on the catalytic characteristics and to study the structure of Pd–Cu nanoparticles by X-ray diffraction (XRD) analysis. The XRD analysis and transmission electron microscopy (TEM) data indicated the formation of uniform bimetallic Pd–Cu nanoparticles (d = 20–60 nm), whose composition corresponded to a ratio between the metals in the catalyst, and also the absence of monometallic Pd⁰ and Cu⁰ nanoparticles. The study of catalytic properties in the liquid-phase hydrogenation of diphenylacetylene (DPA) showed that the activity of the catalysts rapidly decreased with the Cu content increase; however, in this case, the yield of a desired alkene compound significantly increased. The selectivity of alkene formation on the catalysts with the ratios Pd: Cu = 1: 3 and 1: 4 was superior to the commercial Lindlar catalyst.     

Current developments in CO2 hydrogenation towards methanol: A review related to industrial application

Regarding the still increasing CO₂ emissions and the accompanied imminent climate change, utilization of CO₂-containing exhaust gases is one of the major opportunities to lower CO₂ emissions while obtaining valuable products in parallel. Methanol as one of today's key platform chemicals can be industrially produced from these exhaust gases by heterogeneously catalyzed CO₂ hydrogenation. This review elaborates why the Cu/ZnO/Al₂O₃ catalyst is still the most promising candidate to catalyze CO₂ hydrogenation from exhaust gases to reduce CO₂ emissions in the short term. It emphasizes catalyst lifetime and deactivation as well as catalyst poisoning, which are significant factors considering the use of impurity-containing exhaust gases. Besides modifications of the Cu/ZnO system, completely different catalysts are discussed regarding their usability and comparability to the conventional Cu/ZnO/Al₂O₃ catalyst.     

Pd Nanoparticles Supported on Triangle-Shaped La2O2CO3 Nanosheets: A New Highly Efficient and Durable Catalyst for Selective Hydrogenation of Cinnamaldehyde to Hydrocinnamaldehyde

A catalyst in which Pd nanoparticles are supported on triangle-shaped La₂O₂CO₃ nanosheets exposing predominantly the (001) planes (Pd/La₂O₂CO₃-TNS; where TNS denotes triangular nanosheets) was prepared by a facile solvothermal method. The Pd/La₂O₂CO₃-TNS catalysts exhibited excellent catalytic activity and recycling stability for hydrogenation of cinnamaldehyde to hydrocinnamaldehyde with turnover frequency of up to 41 238 h⁻¹. This enhanced activity of Pd/La₂O₂CO₃-TNS results from strong metal–support interactions. Structure analysis and characterization demonstrated that surface-oxygen-enriched La₂O₂CO₃-TNS supports exposing (001) planes are beneficial to charge transfer between the Pd nanoparticles and triangle-shaped La₂O₂CO₃ nanosheets and increase the electron density of Pd. Moreover, the modulated electronic states of the Pd/La₂O₂CO₃-TNS catalysts can enhance the adsorption and activation of hydrogen to enhance the hydrogenation activity.     

Intermetallic Pd<Subscript>1</Subscript>–Zn<Subscript>1</Subscript> nanoparticles in the selective liquid-phase hydrogenation of substituted alkynes

A comparative study of the catalytic characteristics of monometallic Pd/α-Al₂O₃ and bimetallic Pd–Zn/α-Al₂O₃catalysts in the liquid-phase hydrogenation of structurally different substituted alkynes (terminal and internal, symmetrical and asymmetrical) was carried out. It was established that an increase in the reduction temperature from 200 to 400 and 600°C led to a primary decrease in the activity of Pd–Zn/α-Al₂O₃ due to the formation and agglomeration of Pd1–Zn1 intermetallic nanoparticles. The Pd–Zn/α-Al₂O₃ catalyst containing Pd1–Zn1 nanoparticles exhibited increased selectivity to the target alkene formation, as compared with that of Pd/α-Al₂O₃. Furthermore, the use of the Pd–Zn/α-Al₂O₃ catalyst made it possible to more effectively perform the kinetic process control of hydrogenation because the rate of an undesirable complete hydrogenation stage decreased on this catalyst.     

Uniformly dispersed copper nanoparticles onto the modified magnetically recoverable nanocatalyst for aqueous synthesis of primary amides

Magnetically recoverable and environmentally friendly Cu‐based heterogeneous catalyst has been synthesized for the one‐pot conversion of aldehydes to their corresponding primary amides. The Fe₃O₄@SiO₂ nanocomposites were prepared by synthesis of Fe₃O₄ magnetic nanoparticles (MNPs) which was then coated with a silica shell via Stöber method. Bi‐functional cysteine amino acid was covalently bonded onto the siliceous shell of nanocatalyst. The Cu^II ions were then loaded onto the modified surface of nanocatalyst. Finally, uniformly dispersed copper nanoparticles were achieved by reduction of Cu^II ions with NaBH₄. Amidation reaction of aryl halides with electron‐withdrawing or electron‐donating groups and hydroxylamine hydrochloride catalyzed with Fe₃O₄@SiO₂@Cysteine‐copper (FSC‐Cu) MNPs in aqueous condition gave an excellent yield of products. The FSC‐Cu MNPs could be easily isolated from the reaction mixture with an external magnet and reused at least 8 times without significant loss in activity.     

CO2 Hydrogenation on Cu/Al2O3: Role of the Metal/Support Interface in Driving Activity and Selectivity of a Bifunctional Catalyst

Selective hydrogenation of CO₂ into methanol is a key sustainable technology, where Cu/Al₂O₃ prepared by surface organometallic chemistry displays high activity towards CO₂ hydrogenation compared to Cu/SiO₂, yielding CH₃OH, dimethyl ether (DME), and CO. CH₃OH formation rate increases due to the metal–oxide interface and involves formate intermediates according to advanced spectroscopy and DFT calculations. Al₂O₃ promotes the subsequent conversion of CH₃OH to DME, showing bifunctional catalysis, but also increases the rate of CO formation. The latter takes place 1) directly by activation of CO₂ at the metal–oxide interface, and 2) indirectly by the conversion of formate surface species and CH₃OH to methyl formate, which is further decomposed into CH₃OH and CO. This study shows how Al₂O₃, a Lewis acidic and non‐reducible support, can promote CO₂ hydrogenation by enabling multiple competitive reaction pathways on the oxide and metal–oxide interface.     

Metal–Organic Framework-Encapsulated CoCu Nanoparticles for the Selective Transfer Hydrogenation of Nitrobenzaldehydes: Engineering Active Armor by the Half-Way Injection Method

A novel armor-type composite of metal–organic framework (MOF)-encapsulated CoCu nanoparticles with a Fe₃O₄ core (Fe₃O₄@SiO₂-NH₂-CoCu@UiO-66) has been designed and synthesized by the half-way injection method, which successfully serves as an efficient and recyclable catalyst for the selective transfer hydrogenation. In this half-way injection approach, the pre-synthetic Fe₃O₄@SiO₂-NH₂-CoCu was injected into the UiO-66 precursor solution halfway through the MOF budding period. The formed MOF armor could play a role of providing significant additional catalytic sites besides CoCu nanoparticles, protecting CoCu nanoparticles, and improving the catalyst stability, thus facilitating the selective transfer hydrogenation of nitrobenzaldehydes into corresponding nitrobenzyl alcohols in high selectivity (99 %) and conversion (99 %) rather than nitro group reduction products. Notably, this method achieves the precise assembly of a MOF-encapsulated composite, and the ingenious combination of MOF and nanoparticles exhibits excellent catalytic performance in the selective hydrogen transfer reaction, implementing a “1+1>2” strategy in catalysis.     

Tetrametallic Copper Complex to Nanoscale Copper: Selective and Switchable Dehydrogenation-Hydrogenation under Light

A discrete, photoactive, ultrafine copper nanocluster of fewer than hundreds of atoms with stimuli-responsive switchable redox-active states is highly desired to control two different antagonistic reactions. Herein, a mixed-valent tetrametallic copper complex ( C-1 ) of N−O-N Schiff base ligand is disclosed, in which the five different Cu−Cu interactions were used to generate photoactive nanoscale copper [LCu⁰_n, S-1 ] through the reduction of coordinated imine to the amine of C-1 . The presence of a ligand provides stability and helps to homogenize the material ( S-1 ) in the organic solvent. The cluster showed stimuli (O₂/light)-responsive switching between its reduced ( S-1 ) and oxidized [LCu⁰_n−mCuO_m, S-2 ] states that allows it to serve as a highly and poorly active (bistate, relative rate >5–12 fold) catalyst for the dehydrogenation of alcohols to aldehydes and hydrogenation of nitroaromatics to amino aromatics under the light.     

介孔载体负载Pt催化剂上α-酮酸酯的不对称氢化

以介孔材料SBA-15、经或未经Al2O3修饰的具有三维立方孔道结构的SiO2为载体,制备了负载型Pt催化剂,并用于催化α-酮酸酯底物2-氧代-4-苯基-丁酸乙酯(EOPB)和丙酮酸乙酯(Etpy)的不对称氢化反应中.结果表明,当SBA-15孔径由6.2,7.6和9.2nm依次增加时,EOPB不对称氢化的活性和手性选择...     

Thermolysis characteristics of salts of <Emphasis Type="Italic">o</Emphasis>-phthalic acid with the formation of Fe,Co, Ni,Cu metal particles

Studies of the thermolysis of ortho-[Ni(H₂O)₂(C₈H₄O₄)](H₂O)₂, [Cu(H₂O)(C₈H₄O₄)], and acid [M(H₂O)₆](C₈H₅O₄)₂ (M(II) = Fe(II), Co(II), and Ni(II)), [Cu(H₂O)₂(C₈H₅O₄)₂] phthalates reveal that the solid products of their decomposition are composites with nanoparticles embedded in carbon–polymer matrices. Metallic nanoparticles with oxide nanoparticle impurities are detected in iron/cobalt polymer composites, while nickel/copper composites are composed of only metallic particles. It is found that nickel nanoparticles with the diameters of 6–8 nm are covered with disordered graphene layers, while the copperbased composite matrix contains spherical conglomerates (50–200 nm) with numerous spherical Cu particles (5–10 nm).     

Synergic effect of palladium-based bimetallic catalysts for the hydrogenation of nitroaromatics

Bimetallic catalysts, PdCl₂-MX_n and PdCl₂(PhCN)₂-Mx_n (MX_n=FeCl₃, Fe(acac)₃, Co(OAc)₂, CoCl₂, Co(acac)₂, NiCl₂, Ni(OAc)₂, RuCl₃, Cu(OAc)₂, CuCl₂), exhibit remarkable synergic effect which can obviously increase the activity of the monometallic Pd catalyst for the hydrogenation of nitroaromatics, whereas MX_n alone is not catalytically active under the same reaction conditions.     

Magnetically recyclable nano copper/chitosan in O‐arylation of phenols with aryl halides

Interaction of chitosan (CS) with Fe₃O₄, followed by embedding Cu nanoparticles (NPs) on the magnetic surface through adsorption of Cu²⁺, and its reduction to Cu^o via NaBH₄, offers a reusable efficient catalyst (Fe₃O₄/CS‐Cu NPs) that is employed in cross‐coupling reactions of aryl halides with phenols, which affords the corresponding diaryl ethers, with good to excellent yields. The catalyst is completely recoverable from the reaction mixture by using an external magnet. It can be reused four times, without significant loss in its catalytic activity.     

Methanol‐Assisted Autocatalysis in Catalytic Methanol Synthesis

Catalytic methanol synthesis is one of the major processes in the chemical industry and may grow in importance, as methanol produced from CO₂ and sustainably derived H₂ are envisioned to play an important role as energy carriers in a future low‐CO₂‐emission society. However, despite the widespread use, the reaction mechanism and the nature of the active sites are not fully understood. Here we report that methanol synthesis at commercially applied conditions using the industrial Cu/ZnO/Al₂O₃ catalyst is dominated by a methanol‐assisted autocatalytic reaction mechanism. We propose that the presence of methanol enables the hydrogenation of surface formate via methyl formate. Autocatalytic acceleration of the reaction is also observed for Cu supported on SiO₂ although with low absolute activity, but not for Cu/Al₂O₃ catalysts. The results illustrate an important example of autocatalysis in heterogeneous catalysis and pave the way for further understanding, improvements, and process optimization of industrial methanol synthesis.     

Methanol-Assisted Autocatalysis in Catalytic Methanol Synthesis

Catalytic methanol synthesis is one of the major processes in the chemical industry and may grow in importance, as methanol produced from CO₂ and sustainably derived H₂ are envisioned to play an important role as energy carriers in a future low-CO₂-emission society. However, despite the widespread use, the reaction mechanism and the nature of the active sites are not fully understood. Here we report that methanol synthesis at commercially applied conditions using the industrial Cu/ZnO/Al₂O₃ catalyst is dominated by a methanol-assisted autocatalytic reaction mechanism. We propose that the presence of methanol enables the hydrogenation of surface formate via methyl formate. Autocatalytic acceleration of the reaction is also observed for Cu supported on SiO₂ although with low absolute activity, but not for Cu/Al₂O₃ catalysts. The results illustrate an important example of autocatalysis in heterogeneous catalysis and pave the way for further understanding, improvements, and process optimization of industrial methanol synthesis.     

Support Morphology Effect on Selective Hydrogenation of 3-Nitrostyrene to 3-Vinylaniline over Pt/α-Fe2O3 Catalysts

Selective hydrogenation of substituted nitroaromatic compounds is an extremely important and challenging reaction. Supported metal catalysts attract much attention in this reaction because the properties of metal nanoparticles (NPs) can be modified by the nature of the support. Herein, the support morphology on the catalytic performance of selective hydrogenation of 3-nitrostyrene to 3-vinylaniline was investigated. Pt NPs supported on octadecahedral α-Fe₂O₃ supports with a truncated hexagonal bipyramid shape (Pt/α-Fe₂O₃-O) and rod-shaped α-Fe₂O₃ supports (Pt/α-Fe₂O₃-R) were prepared by glycol reduction method. Detailed characterizations reveal that the electronic structure and dispersion of Pt NPs can be modified by the supports. The Pt/α-Fe₂O₃-O catalyst exhibited superior catalytic performance for hydrogenation of 3-nitrostyrene because of its low coordinated Pt sites and the small Pt NPs size, which is benefit from the high-index exposed surfaces of truncated hexagonal bipyramid-shaped α-Fe₂O₃ support. The structural evolution during the catalytic reaction was investigated in detail by identical location transmission electron microscopy (IL-TEM) method, which found that the high cycling activity of Pt/α-Fe₂O₃-O catalyst during the cycle experiment results from the stability of Pt NPs.